# WebSocket API Specification

## Overview

This document specifies the WebSocket API for real-time blockchain data subscriptions, including new blocks, pending transactions, and address activity.

**Endpoint**: `wss://api.explorer.d-bis.org/ws`

## Connection Lifecycle

### Connection

**URL**: `wss://api.explorer.d-bis.org/ws?chain_id=138`

**Query Parameters**:
- `chain_id` (optional): Default chain ID for subscriptions
- `api_key` (optional): API key for authenticated connections

**Headers**:
- `Authorization: Bearer <token>` (optional)

### Authentication

**Methods**:
1. Query parameter: `?api_key=<key>`
2. Header: `Authorization: Bearer <token>`
3. Message: Send auth message after connection

**Auth Message**:
```json
{
  "type": "auth",
  "api_key": "your-api-key"
}
```

**Response**:
```json
{
  "type": "auth_success",
  "user_id": "uuid",
  "tier": "pro"
}
```

### Heartbeat

**Purpose**: Keep connection alive and detect disconnections.

**Client Ping**: Send every 30 seconds
```json
{
  "type": "ping"
}
```

**Server Pong**: Response within 1 second
```json
{
  "type": "pong",
  "timestamp": 1640995200
}
```

**Timeout**: Connection closed if no pong received within 60 seconds

## Subscription Model

### Subscribe to New Blocks

**Request**:
```json
{
  "type": "subscribe",
  "channel": "blocks",
  "chain_id": 138,
  "params": {
    "include_transactions": false
  }
}
```

**Response**:
```json
{
  "type": "subscribed",
  "subscription_id": "sub_123",
  "channel": "blocks"
}
```

**Updates**:
```json
{
  "type": "update",
  "subscription_id": "sub_123",
  "data": {
    "number": 12345,
    "hash": "0x...",
    "timestamp": "2024-01-01T00:00:00Z",
    "transaction_count": 100
  }
}
```

### Subscribe to Pending Transactions

**Request**:
```json
{
  "type": "subscribe",
  "channel": "pending_transactions",
  "chain_id": 138,
  "params": {
    "from_address": "0x...",  // Optional filter
    "min_value": "1000000000000000000"  // Optional filter
  }
}
```

**Updates**: Transaction objects as they enter mempool

### Subscribe to Address Activity

**Request**:
```json
{
  "type": "subscribe",
  "channel": "address",
  "chain_id": 138,
  "params": {
    "address": "0x..."
  }
}
```

**Updates**: Transactions involving the address

### Subscribe to Logs/Events

**Request**:
```json
{
  "type": "subscribe",
  "channel": "logs",
  "chain_id": 138,
  "params": {
    "address": "0x...",
    "topics": ["0xddf252..."]  // Event signatures
  }
}
```

**Updates**: Matching log entries

### Unsubscribe

**Request**:
```json
{
  "type": "unsubscribe",
  "subscription_id": "sub_123"
}
```

**Response**:
```json
{
  "type": "unsubscribed",
  "subscription_id": "sub_123"
}
```

## Message Formats

### Client Messages

**Subscribe**:
```json
{
  "type": "subscribe",
  "channel": "<channel_name>",
  "chain_id": 138,
  "params": { ... }
}
```

**Unsubscribe**:
```json
{
  "type": "unsubscribe",
  "subscription_id": "<id>"
}
```

**Ping**:
```json
{
  "type": "ping"
}
```

### Server Messages

**Update**:
```json
{
  "type": "update",
  "subscription_id": "<id>",
  "data": { ... }
}
```

**Error**:
```json
{
  "type": "error",
  "code": "invalid_subscription",
  "message": "Invalid subscription parameters",
  "subscription_id": "<id>"
}
```

**Notification**:
```json
{
  "type": "notification",
  "level": "info",  // info, warning, error
  "message": "Subscription limit reached"
}
```

## Subscription Limits

**Per Connection**:
- Anonymous: 5 subscriptions
- Free API Key: 20 subscriptions
- Pro API Key: 100 subscriptions
- Enterprise: Unlimited

**Per Chain**:
- Limit subscriptions per chain to prevent abuse

## Reconnection Strategy

### Automatic Reconnection

**Strategy**: Exponential backoff

**Backoff Schedule**:
- Initial: 1 second
- Max: 60 seconds
- Multiplier: 2x

**Behavior**:
- Reconnect automatically
- Resubscribe to all active subscriptions
- Resume from last received update

### Manual Reconnection

**Steps**:
1. Close connection gracefully
2. Reconnect with same parameters
3. Resubscribe to desired channels

## Rate Limiting

**Limits**:
- Message rate: 10 messages/second per connection
- Subscription rate: 5 subscriptions/minute per connection
- Update rate: Throttled per subscription type

**Throttling**: Server may batch or skip updates if client cannot keep up

## Error Codes

- `invalid_message`: Malformed message
- `invalid_subscription`: Invalid subscription parameters
- `subscription_limit`: Too many subscriptions
- `rate_limit`: Rate limit exceeded
- `unauthorized`: Authentication required
- `chain_not_supported`: Chain ID not supported
- `internal_error`: Server error

## Security Considerations

### Connection Security

- WSS (WebSocket Secure) required
- TLS 1.2+ only
- Certificate validation

### Authentication

- API key validation
- User permission checks
- Subscription authorization

### Message Validation

- Validate all incoming messages
- Sanitize parameters
- Reject invalid requests

## Performance Considerations

### Message Batching

**Strategy**: Batch multiple updates into single message when possible

**Example**:
```json
{
  "type": "batch_update",
  "updates": [
    { "subscription_id": "sub_1", "data": {...} },
    { "subscription_id": "sub_2", "data": {...} }
  ]
}
```

### Backpressure

**Strategy**: Drop updates if client cannot process them

**Indicators**:
- Client buffer full
- No ping/pong responses
- Slow message processing

## References

- REST API: See `rest-api.md`
- GraphQL API: See `graphql-api.md`
- Mempool Service: See `../mempool/mempool-service.md`